1. Field of the Disclosure
The present disclosure relates to a blowing agent in the form of a solid mixture of an inorganic powder, more particularly nanoparticles of an inorganic carbonate, and an acid. The acid is capable of being liquefied by heating to be reactive with the carbonate to release carbon dioxide that is useful as a blowing agent in all types of organic foams. The solid mixture, optionally pelletized in a suitable polymer carrier, is useful as a heat-activated blowing agent additive in polymer compositions.
2. Description of the Related Art
Lower cost bicarbonates which generate CO2 are employed as blowing agents, but the results achieved during their thermal decomposition are relatively unpredictable, and therefore they are not usually employed to produce high quality polymer foam parts having evenly distributed porosity and aesthetic appeal.
A wide variety of compounding and blending methods are well-known and commonly used in the art and most may be adapted to mix and compound with the components of foamable polyolefin or polystyrene formulations disclosed herein. Modifying components that are not thermally sensitive, whether in powder, pellet, or other suitable form, may be mixed and melt compounded using a high shear mixer, e.g., a twin-screw extruder at temperatures effective to render the resinous components molten and obtain a desirably uniform blend. Thermally sensitive components of the formulations, including blowing agents, may be physically mixed with the resin in powder or pellet form using conventional dry-blending methods just prior to feeding the mixture to the extruder.
In a typical method for combining inorganic powder blowing agents and polymers, the powder and polymer are dropped through a feed tube into the feed barrel near the starting end of an extruder or into a “side stuffer” part-way along the extruder's length. The combined powders and polymers are compounded and extruded. In another typical method for combining inorganic powders and polymers, the inorganic powder can be dropped with the polymer into the cavity of a rotational blender such as a Banbury® mixer. The relative quantities of the polymer(s), blowing agent(s) and other additives, as well as the temperature and the manner in which pressure is reduced, will tend to affect the qualities and properties of the resulting foam product.
Conventional blowing agents produce foams that contain cells that have a negative impact upon the structural strength and appearance of the foamed product. It is desirable to produce thermoformed foamed products that are aesthetically pleasing, have a high degree of porosity and a smooth surface, and are lightweight while maintaining structural strength. Such products would be environmentally and ecologically desirable as these products require a comparatively reduced amount of resin in the production of the finished product.